Question:

You deal and open 1. Partner responds 1NT. You might play that as forcing, semi-forcing, or "nothing special". You need to make sure you and partner are on the same page. For our answer, we'll assume semi-forcing which means partner has up to 12 points and we are allowed to pass.

What is your action after 1NT with: 

KJ765
K2
KQ2
KQJ

Answer:

2NT. This shows 18-19 HCP and a balanced hand. We can't have 15-17 and a balanced hand, because we would have opened 1NT. With 12-14 and a balanced hand, we would pass.